The problem with DC's other big "JLA worthy" heroes is that different characters have held the ranks at different times, which hurts the public's awareness of who they are.
The Flash and the Green Lantern can each be four or five different people depending on what decade you remember. Jay Garrick, Barry Allen, Wally West, or Bart Allen? Alan Scott, Hal Jordan, Guy Gardner, John Stewart or Kyle Rayner? Is Hawkman an alien or a reincarnated Egyptian? Or do you go with Hawkwoman? Martian Manhunter is a great character, but I think he'd work best in a Justice League film.
Likewise, while Wonder Woman has a TV show people remember, the general person on the street can't name any of the villains from her rogues gallery or explain her origin story in detail, or even say what powers she has beyond her magical equipment. It would take a strong director to hammer out her story into something that resonates with the people at large.
Now let me be clear, I'd love to see individual Green Lantern, Flash, or Wonder Woman movies, but until Warner Bros really sets their sights on making the films happen, they won't happen.
Also, while Aquaman is actually a cool character the Super Friends cartoon basically killed him.